@PotomacBobThink of the fresh, lush growth of spring alfalfa, just coming into bloom. Higher ratio of leaf to stem, and cut while the stems are young and tender. Properly air-cured and baled, the result is a lush greenish hay that is resistant to shatter when handling. It is by far more palatable and nutritious. That, coupled with the fact that the rancher is quick to harvest it so the second growth will follow, avoids letting the growth become 'stemmy' and not so palatable.
The second cutting can be very good hay if harvested soon enough. But the third cutting, if there is one, is usually the result of letting it grow, and grow late into the season, so it's mostly hard stems and smaller leaves, meaning the ratio of tender leaf to thick stem is skewed.
In the high mountain valley where I worked summers raking hay, baling it, and loading and stacking the bales while in high school, ranchers got only two cuttings; and frequently that second cutting was not as good... thus bringing a lower price, or serving as 'homestead feed' for one's own cattle.
Living here on the coast, I've seen too much really dreadful hay harvests, mostly stems with the brittle leaves shattered and lost, because of too many rain showers and the cut hay laying in the field too long before it's dry enough to bale. I s'pect that's why the new "haylage" method of cutting and bagging to make field-cured hay silage is so popular.
Been there, lived it, done it.